Module system for manufacturing two and three stable positions fluid-operated actuators

ABSTRACT

In a module system for manufacturing variants of two and three stable positions fluid-operated actuators a cylinder housing of both variants of two and three stable positions actuators are manufactured from a blank, including at least one opening for the cover and being identical for the variants of said two and three stable position actuator, and being at least prepared for the arrangement of:
         a first pressure duct,   a second pressure duct, and   a first cylinder diameter of the cylinder housing, thus decreasing manufacturing costs.

BACKGROUND AND SUMMARY

The present invention relates to actuators operated by fluid pressure,and more particularly to a manufacturing module system for havingvariants thereof with two and three stable positions.

Fluid-operated actuators, that is, actuators that are operated withfluid pressure are widely used. Some examples are hydraulic cylinders inexcavators and pneumatic cylinders in production automation equipment.In transmissions for heavy trucks and buses, pneumatic actuators areoften used for automation, fully or in part, of the gear shifting.

Simplified, a simple fluid-operated actuator is composed of a cylinderhousing, at least one cover and a piston that is fixedly connected to apiston rod. The piston is located inside the cylinder housing and cover.Thereby two pressure chambers are created, one on each side of thepiston. A sealing arrangement allows a difference in pressure betweenthese chambers. By applying fluid pressure in either chamber, force isapplied on the piston that will urge to move. The cylinder housing andcover allow axial motion of the piston and piston rod between two endpositions. These end positions will be referred to as stable positions.They correspond to equilibrium positions when fluid pressure is appliedin either chamber.

For special purposes, more complex fluid-operated actuators have beendeveloped. More than two stable positions have been achieved by means ofmore chambers and additional coaxial pistons. These additional pistonshave a limited axial motion possible relative to both the cylinderhousing and the piston rod.

A typical transmission for a heavy truck is shown in EP1035357. In orderto achieve a large number of useful gear ratios with a limited number ofgearwheels, the transmission is composed of three main functional units;a splitter section 34, a main section 35 and a range section 38. Thesplitter section provides two possible paths of transmitting the powerfrom an input shaft 2 to a countershaft 4. Which of these paths that isactive is determined by a double-acting tooth clutch (“synchronisedcoupling”) 12. The main section 35 provides several possible paths oftransmitting the power from the countershaft 4 to a main shaft(“intermediate shaft”) 3. A number of tooth clutches 18, 20 and 32 canbe engaged, one at a time, to make these paths active. Finally, therange section 38 can be regarded as a two-speed gearbox that isconnected in series with the main section 35. The range section has aspeed reduction gear, normally referred to as low range, and a directgear, high range, that has no speed change. The position of a toothclutch sleeve 44 determines which range gear that is active.

In most heavy truck transmissions, the splitter section and the rangesection are operated by pneumatic actuators. Conventionally, the toothclutch in the splitter section has two stable positions, one for each ofsaid paths. Likewise, the range section tooth clutch conventionally hastwo stable positions, one for high range and one for low range. Thus, inthe conventional case the splitter section and the range section caneach be operated by a simple pneumatic actuator that has two stablepositions.

In recent years, solutions have been presented that would make itadvantageous in some cases to use a middle, neutral, position in thesplitter section or the range section. EP1035357 presents a splittersection with a neutral position that is used to reduce the risk ofdamaging the transmission at some inappropriate shifts. However, such adevice would not be necessary for some designs of gear lever and shiftpattern for the main section. Neither would it be required for automatedvariants of the transmission in question.

Furthermore, EP1055845 presents a range section that has a neutralposition. This is used to reduce the effort at manual main sectionshifts, and it enables the use of smaller and less costly toothclutches. It would also facilitate the use of simple centrifugalclutches, like the one presented in US-2004/0262115, since the clutchdoes not need to be disengaged during a main section shift. However, theshift time might increase, and the use in automated variants can bequestioned.

In conclusion, splitter sections and range sections with a neutralposition may not be used in all variants of a heavy truck transmissionfamily. In some cases, it would make sense to use the simplerconventional design with two stable positions and no neutral position.

So, there is a need for a way to enable variants with two or threestable positions of fluid-operated actuators in a cost-efficient way.According to an aspect of the present invention, substantially the sameblank is used for the cylinder housings of the actuator variants withtwo and three stable positions. In a first embodiment the invention ischaracterized in that said blank comprises at least one opening for saidcover and that it is identical for said variants of said two and threestable position actuator, and that the blank is at least prepared forthe arrangement of:

-   -   a first pressure duct,    -   a second pressure duct and    -   a first cylinder diameter of said cylinder housing.

It can be noted that the cylinder housing in general is a large andfairly expensive part whose blank requires a complex and costly tool.The cylinder housing blank can be, for instance, cast, forged, extruded,pressed or injection moulded. The blank will be finished to a cylinderhousing by means of operations like milling and honing of cylinder andsealing surfaces, drilling of access ducts to the pressure chambers, andmaking fastening arrangements for the cover. If the same blank can beused for different actuator variants, the costs for tooling can bereduced, and higher production volumes of the blank can be achieved.According to another embodiment of the invention it is also possiblethat at least one of said first and second pressure ducts and said firstcylinder diameter are finally produced with same set of tools creatingsame dimensions for said at least one of said first and second pressureducts and said first cylinder diameter respectively in both said two andthree stable position variants. According to a further developedembodiment of the invention the same set of tools can be used in bothsaid two and three stable position variants, thus creating samedimensions for said first and second pressure duct and said firstcylinder diameter respectively for all variants.

In a preferred embodiment, the actuator is an integrated part of anactuator unit that comprise, for instance, sensors, other actuators andvalves that control the flow of pressurised fluid to the pressurechambers. The cylinder housing is part of a large housing whose blankrequires very high tooling costs. Thereby, it is of particular advantageto avoid variants of the blank.

In another preferred embodiment, the variant with three stable positionsis designed with a main piston, which is fixedly attached to the pistonrod, and a ring piston with limited axial motion relative to the mainpiston. There are three cylinder-piston system diameters, one smallbetween said main and ring pistons, one larger for the main pistonalone, and one even larger for the ring piston alone. This largestdiameter is identical to the cylinder-piston diameter of the variantwith two stable positions. This gives a compact design withsubstantially equal actuator strokes between the end positions for thevariants with two and three stable positions.

In still another preferred embodiment, there is a ring-shaped protrusionin the cover for the variant with three stable positions. The innerperiphery of this protrusion serves as the outer part of acylinder-piston system for the main piston and one of the pressurechambers. A duct between the inner and outer peripheries form a part ofthe supply duct to said pressure chamber. The outer periphery of theprotrusion also forms part of sealing devices between an intermediatechamber, said supply duct and the ambient air. With this design, therequired different cylinder-piston diameters are achieved in aconvenient way.

In yet another preferred embodiment, on said outer periphery betweensaid supply duct and said intermediate chamber, the sealing device has alarger diameter than the cylinder-piston system diameter of the variantwith two stable positions. Thereby, said intermediate chamber can have abreathing duct in the cylinder housing that will not risk damaging thesealing device of said large-diameter cylinder-piston system of saidring piston.

In a further preferred embodiment, the devices that guide and centre theaxial motion of said ring piston are axially spaced apart. This willimprove the stability of that motion.

In an additional preferred embodiment, the breathing duct for theintermediate chamber is located in the cover. Thereby, the cylinderhousing can be the same for both two and three stable position variants.

In an alternative preferred embodiment, the breathing duct is located inthe main piston and piston rod. The cylinder housing can be the same forboth two and three stable position variants here, too. Moreover, if themain piston is attached to the piston rod with a hollow pin, that pincould be a part of the breathing duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be exemplified by means of the enclosed drawings.

FIG. 1 shows a schematic longitudinal section of a typicalfluid-operated actuator with two stable positions, which as such is anexample of prior art, but which also is part of the inventive modulesystem.

FIGS. 2 a, 2 b and 2 c show a schematic longitudinal section of atypical fluid-operated prior art actuator with three stable positions ineach of these three stable positions.

FIG. 3 shows an embodiment of the invention with a ring-shapedprotrusion on the cover.

FIG. 4 shows an embodiment of the invention where the ring piston hasits guiding devices located at different axial positions and where thereis an increased diameter for the sealing device between the intermediatechamber and the pressure duct to the left pressure chamber.

FIG. 5 shows an embodiment of the invention with modified ring pistonand with breathing ducts for the intermediate chamber located in thecover and in the main piston and piston rod.

FIG. 6 shows an embodiment of the invention where the main piston isattached to the piston rod with a hollow pin that forms a part of thebreathing duct for the intermediate chamber.

DETAILED DESCRIPTION

FIG. 1 shows a simplified longitudinal section of a fluid-operatedactuator 101 with two stable positions, which actuator forms a part ofthe inventive module system and which as such can be regarded asconventional technique, comprising a cylinder housing 102, piston 103,piston rod 104 and cover 105. The cylinder housing 102 and the cover 105are axially connected in a not showed way. Thereby, the cylinder housing102, piston rod 104 and cover 105 will enclose a left pressure chamber106 and a right pressure chamber 107 on either side of the piston 103.The cylinder housing 102 has a left supply duct 108 and a right supplyduct 109 that are in fluid connection with the left pressure chamber 106and right pressure chamber 107, respectively. Valves (not shown) connectthe left supply duct 108 and right supply duct 109 to either a pressuresupply or to an exhaust of ambient pressure.

In FIG. 1 the right supply duct 109 is connected to the pressure supply.Thereby, the right pressure chamber 107 is filled with pressurized fluidand a fluid pressure acts on the piston 103. The left supply duct 108 isconnected to the exhaust, and hence there is ambient pressure in theleft pressure chamber 106. So, the piston 103 and piston rod 104 areurged to move to the left. The leftwards motion is stopped when the leftend stop abutment 103 a of the piston 103 comes into contact with themating part of the cover 105. This represents the left stable positionof the actuator 101. Similarly, if the left supply duct 108 wereconnected to the pressure supply and the right supply duct 109 wereconnected to the exhaust, then the piston 103 and piston rod 104 wouldbe urged to the right. The right stable position would then be reachedwhen the right end stop abutment 103 b of the piston 103 is in contactwith the mating part of the cylinder housing 102.

In order to prevent leakage between the pressure chambers and thesurroundings, sealing devices are required. Sealing devices can be ofany of different available types, as readily known by a person skilledin the art, for instance elastomeric lip seal type. Furthermore, forproper function the axially moving parts, as the piston 103 and pistonrod 104, need to be centred and kept substantially coaxial with themating parts of the cylinder housing 102 and cover 105. This is achievedby means of guiding devices that can be of various types, for instancepolymeric guide bands or ball bushings, as would be known by a personskilled in the art. A sealing device may be integrated with a guidingdevice, but may also be separate. In case of separate, non-integrated,sealing and guiding devices, they may be located close to each other orwide apart. They may even act on different surfaces, as would berecognized by a person skilled in the art. In the figures of the presentdocument, the guiding devices are left out, for simplicity, or can beregarded as integrated in the sealing devices, where appropriate. So, inFIG. 1 there is a static sealing device 111 (e.g. o-ring or gasket) toprevent leakage between the cylinder housing 102 and cover 105 from theleft pressure chamber 106. Moreover, a left rod sealing device 112prevents leakage between the cover 105 and piston rod 104. Similarly, aright rod sealing device 113 prevents leakage between the cylinderhousing 102 and piston rod 104 from the right pressure chamber 107.

Finally, a piston sealing device 114 on the outer periphery of thepiston 103 prevents leakage between the pressure chambers 106 and 107.

In the right pressure chamber 107, the fluid pressure acts on the piston103 on an effective ring-shaped area defined by a cylinder-piston systemdiameter 103 d and a piston rod diameter 104 d. The actuator 101 has itspiston rod 104 extending out of the cylinder housing 102 and cover 105on both sides. This is a general case, designs where the piston rodextends out on one side, only, are also common. In such a case, thepressure in one of the pressure chambers will act on an effectivecircular area defined by the cylinder-piston system diameter 103 d.

FIGS. 2 a, 2 b and 2 c show a prior art fluid-operated actuator 210 withthree stable positions. A cylinder housing 202 and a cover 205 enclose amain piston 203, which is fixedly attached to a piston rod 204, and aring piston 221. The cylinder housing 202, main piston 203 and pistonrod 204 enclose a left pressure chamber 206 where the pressure can acton the main piston 203 on an effective ring-shaped area defined by amain cylinder-piston system diameter 203 d and a piston rod diameter 204d. The ring piston 221 is located on the outside of an axial extension203 e of the main piston 203. The axial motion of the ring piston 221 islimited by diameter steps in the cylinder housing 202, main piston 203and cover 205. A right pressure chamber 207 is enclosed by the cylinderhousing 202, main piston 203, piston rod 204, cover 205, and ring piston221. A pressure in the right pressure chamber 207 will act on the ringpiston 221 on an effective ring-shaped area defined by an outercylinder-piston system diameter 221 d (between the cylinder housing 202and ring piston 221) and an inner cylinder-piston system diameter 221 i(between the ring piston 221 and axial extension 203 e of the mainpiston 203). Furthermore, a pressure in the right pressure chamber 207will act on the main piston 203 on an effective ring-shaped area definedby the inner cylinder-piston system diameter 221 i and the maincylinder-piston system diameter 203 d and a piston rod diameter 204 d.Between the left pressure chamber 206 and the right pressure chamber 207there is an intermediate pressure chamber 222 enclosed by the cylinderhousing 202, main piston 203 and ring piston 221.

The left pressure chamber 206 is in fluid connection with a left supplyduct 208. Similarly, the right pressure chamber 207 is in fluidconnection with a right supply duct 209. Valves (not shown)’ connect thesupply ducts 208 and 209 to either a pressure supply or to an exhaust ofambient pressure. The intermediate chamber 222 is not to be pressurized;hence a breathing duct 223 in the cylinder housing 202 connects it toambient pressure.

A static sealing device 211 prevents leakage between the cylinderhousing 202 and cover 205 from the left pressure chamber 206. A left rodsealing device 212 prevents leakage between the cylinder housing 202 andpiston rod 204. Similarly, a right rod sealing device 213 preventsleakage between the cover 205 and piston rod 204 from the right pressurechamber 207. A main piston sealing device 214 on the outer periphery ofthe main piston 203 prevents leakage between the left pressure chamber206 and the intermediate chamber 222 at the main cylinder-piston systemdiameter 203 d. On the ring piston 221 there are two sealing devicesthat prevent leakage between the right pressure chamber 207 and theintermediate chamber 222; an inner ring piston sealing device 215 at theinner cylinder-piston system diameter 221 i and an outer ring pistonsealing device 216 at the outer cylinder-piston system diameter 221 d.

In FIG. 2 a the left pressure chamber 206 is pressurized. The fluidpressure will urge the main piston 203 and piston rod 204 to the right.A right stable position is reached when the right end stop abutment 203b of the main piston 203 is in contact with the mating part of the cover205.

In FIG. 2 b the right pressure chamber 207 is pressurized. The fluidpressure has urged the main piston 203 and piston rod 204 to a leftstable where the left end stop abutment 203 a of the main piston 203 isin contact with the mating part of the cylinder housing 202.

Finally, in FIG. 2 c both the left pressure camber 206 and rightpressure chamber 207 are pressurized. A middle stable position isthereby reached when the ring piston 221 mates with a housing diameterstep abutment 202 a in the cylinder housing 202 and with a pistondiameter step abutment 203 a on the main piston 203. The pressure in theleft pressure chamber 206, acting between diameters 203 d and 204 d,cannot alone push the main piston 203 to the right of this position,since that would lift the ring piston 221 off the housing diameter stepabutment 202 a. That motion would be counteracted by the pressure in theright pressure chamber 207 that acts on the larger area betweendiameters 221 d and 204 d. Analogously, a motion of the main piston 203to the left of the middle stable position would axially separate thering piston 221 from the piston diameter step abutment 203 a. Thus, thepressure in the right pressure chamber 207, acting between diameters 221i and 204 d, cannot alone push the main piston 203 left of the middlestable position, since that would be counteracted by the left pressurechamber 206 whose pressure acts on the larger area between diameters 203d and 204 d.

FIG. 3 shows a fluid-operated actuator 301 with three stable positionsthat is a variant of the plain actuator 101 in FIG. 1, and thus part ofthe inventive module system. The cylinder housing 102 a has beenmodified with an additional breathing duct 323 for the intermediatechamber 322. A cover 305 is fixedly attached to, mated against or,preferably, integral with a ring-shaped protrusion 305 p, whose innerperiphery forms the cylinder-piston sealing diameter 303 d for the leftpressure chamber 306 and main piston 303 with sealing device 314. Thereis a cover supply duct 305 c in the cover 305 that provides a fluidconnection between the left supply duct 108 and the left pressurechamber 306. A cover abutment 305 a defines the middle stable positionfor a ring piston 321. Leakage from the supply ducts 108 and 305 c areprevented by static sealing devices 111 and 111 a. The originalcylinder-piston system diameter 103 d of the cylinder housing 102 servesin the variant 102 a as the sealing diameter for the static sealingdevice 111 a and as the cylinder-piston system diameter for the rightpressure chamber 307 and outer sealing device 316 of the ring piston321. An inner sealing device 315 acts at cylinder-piston system diameter321 i on an extension 303 e of the main piston 303.

The difference between the original cylinder housing 102 of the plainactuator 101 and the cylinder housing 102 a is minimal. The breathingduct 323 for the intermediate chamber 322 has been added in the cylinderhousing 102 a. Thereby, according to the invention, the same blank canbe used for both cylinder housings 102 and 102 a. That will save toolingcosts and facilitate the use of variants with two and three stablepositions. That is especially the case when the cylinder housings 102and 102 a are integrated with other parts, for instance a gear-shiftcontrol unit in a vehicle transmission, and, hence, would requirecomplex and expensive tooling.

In the fluid-operated actuator 301 in FIG. 3 the cylinder-piston systemdiameter 103 d of the cylinder housing 102 a is used for the outersealing device 316 of ring piston 321 as well as for the static sealingdevice 111 a. That may facilitate the manufacturing of the cylinderhousing blank and the machining thereof. However, edges and burrs mayoccur where the breathing duct 323 ends at the cylinder-piston systemdiameter 103 d. This will pose a risk of damaging the outer sealingdevice 316 at the assembly, when the seal surface will pass over the endof the breathing duct 323.

This is solved in the modified actuator 401 in FIG. 4, which actuatoralso forms part of the inventive module system. There, the cylinderhousing 102 b has a larger diameter 102 d where the breathing duct 423for the intermediate chamber 422 ends. Hence, the risk of damaging theouter sealing device 316 at the assembly has been reduced greatly.Furthermore, the diameter 102 d could be used for both static sealingdevices 111 and 111 b between the cover 405 and the cylinder housing 102b. Then, the static sealing devices 111 and 111 b could be identical,which would save costs.

The ring piston 421 in the actuator 401 has been made wider than thecorresponding ring piston 321 in FIG. 3. Thereby, several advantageshave been gained. Firstly, the large cylindrical surface with diameter103 d in the cylinder housings 102, 102 a and 102 b has been used, sothe volume of the right pressure chamber 407 has been minimized, whichmay improve the dynamic performance of the actuator 401. Secondly, it isno longer possible for the ring piston 421 to move that far to the rightfrom the position in FIG. 4 that the inner sealing device 315 would nolonger be in contact with the extension 303 e of the main piston 303.Thirdly, the larger width of the ring piston 421 has made it possible tolocate the sealing devices 315 and 316, with integrated guiding devices,significantly axially apart from each other. That will improve thestability against misalignment for the ring piston 421.

FIG. 5 shows a further modified actuator 501 of the variant with threestable positions. Actuator 501 also forms part of the inventive modulesystem. There, the ring piston 521 has been extended axially inside thering-shaped protrusion 505 p of the cover 505. Thereby, the guidingdevices are axially located even further apart than the actuator 401 inFIG. 4. Moreover, the inner sealing and guiding device has beenseparated into a pure sealing device 515 s, acting on the innercylinder-piston system diameter 321 i, and a guiding device 515 g thatacts on the inside of the ring-shaped protrusion 505 p. The guidingdevice 515 g thereby acts on the main cylinder-piston system diameter303 d, which is larger and possibly stiffer than for the correspondingsealing and guiding device 315 in FIG. 3. Furthermore, with the ringpiston 521 extending axially inside the ring-shaped protrusion 505 p,the sealing device 515 s will be in contact with the extension 503 e ofthe main piston 503 even for the most extreme relative positions of themain piston 503 and ring piston 521.

FIG. 5 also shows two alternative breathing ducts for connecting theintermediate chamber 522 to ambient pressure. There is a cover breathingduct 523 c in the cover 505 and a piston rod breathing duct composed ofa mainly radial duct 523 p in main piston 503 and a mainly axial duct523 r in piston rod 504. With any of these breathing ducts, the cylinderhousing 102, as a finished part, can be identical for actuator variantswith two and three stable positions.

FIG. 6 shows another embodiment of a piston rod breathing duct in anactuator 601 of the variant with three stable positions, which actuatoralso forms part of the inventive module system. A substantially radialduct 623 p through the main piston 603 and piston rod 604 is formed, atleast in part, by a hollow pin 630 that fixedly connects the main piston603 to the piston rod 604. The duct 623 p is in fluid connection with asubstantially axial duct 623 r in the piston rod 604. This fluidconnection could be achieved with, e.g., a slot or a radial hole 630 hin the hollow pin 630. A corresponding ring piston is here numbered 621.Also in this case the cylinder housing 102, as a finished part, can beidentical for actuator variants with two and three stable positions.

According to further embodiments of the invention it is also possiblethat at least one of said first and second pressure ducts and said firstcylinder diameter are finally produced with same set of tools creatingsame dimensions for said at least one of said first and second pressureducts and said first cylinder diameter respectively in both said two andthree stable position variants. In yet another embodiment of theinvention all of said first and second pressure ducts and said firstcylinder diameter are finally produced with different sets of toolscreating different dimensions for said first and second pressure ductsand said first cylinder diameter respectively, when comparing said twostable position variants with said three stable position variants.However, said blank is still identical for said two and three stableposition variants.

Finally, in a preferred embodiment the actuator is arranged forcontrolling a splitter or range section in a vehicle transmission.

Although the present invention has been set forth with a certain degreeof particularity, it is understood that various modifications,substitutions and rearrangements of the components are possible without’departing from the spirit and scope of the invention as hereinafterclaimed.

1. A module system for manufacturing two and three stable positionfluid-operated actuators, the two stable position actuator comprising afirst piston enclosed by a cylinder housing, where the first pistonbeing fixedly connected to a piston rod that extends axially out throughat least one of the cylinder housing and at least one cover in one oftwo ends of the cylinder housing, at least a first and a second pressureduct in the cylinder housing through which at least two pressurechambers, that are separated by the first piston, can selectively be setin fluid connection with a pressure supply or ambient pressure byvalves, and the three stable position actuator comprising all abovementioned corresponding elements for the two stable position actuatorplus a main piston and a breathing duct, the elements forming togethertwo pressure chambers and a non-pressurized intermediate chamber, thechambers being separated by the main piston and a ring piston, whichring piston corresponds to the first piston, and where the cylinderhousing of the both variants of two and three stable positions actuatorsare manufactured from a blank, wherein the blank comprising at least oneopening for the cover and being identical for the variants of the twoand three stable position actuator, and being at least prepared for thearrangement of: the first pressure duct, the second pressure duct and afirst cylinder diameter of the cylinder housing.
 2. A module system asin claim 1, wherein at least one of the first and second pressure ductsand the first cylinder diameter are finally produced with same set oftools creating same dimensions for at least one of the first and secondpressure duct and the first cylinder diameter respectively in both thetwo and three stable position variants.
 3. A module system as in claim1, wherein the first and second pressure ducts and the first cylinderdiameter are finally produced with same set of tools creating samedimensions for the first and second pressure duct and the first cylinderdiameter respectively in both the two and three stable positionvariants.
 4. A module system as in claim 1, wherein in the variants; thecylinder housing, the first piston and an outer sealing device forsubstantially axial motion compose an outer cylinder-piston system atthe first cylinder diameter, and that there is at least a first staticsealing device between the cylinder housing and the at least one cover.5. A module system as in claim 4, wherein the first static sealingdevice acts on a larger diameter than the first cylinder diameter in oneof the variants.
 6. A module system as in claim 1, wherein in thevariant with three stable positions there is a ring-shaped part as anintegral part of, fixedly connected to, or constantly mated to a firstcover of the at least one cover, and that the inner periphery of thering-shaped part, the main piston and a main sealing device compose amain cylinder-piston system at a main diameter.
 7. A module system as inclaim 6, wherein there is a second static sealing device arrangedbetween the cylinder housing and the outer periphery of the ring-shapedpart.
 8. A module system as in claim 7, wherein the second staticsealing device acts on the first cylinder diameter.
 9. A module systemas in claim 6, wherein the second static sealing device acts on a seconddiameter that is larger than the first cylinder diameter.
 10. A modulesystem as in claim 9, wherein the second diameter is substantially equalto the larger diameter, and that the first and second static sealingdevices are identical.
 11. A module system as in claim 5, wherein in thevariant with three stable positions the ring piston is arranged withlimited axial motion relative to the main piston, and that the innerperiphery of the ring piston along with an inner sealing device and anextension that is integral with, or fixedly connected to, the mainpiston compose an inner cylinder-piston system at an inner diameter. 12.A module system as in claim 11, wherein the inner sealing device and theouter sealing device are arranged at axially separated positions.
 13. Amodule system as in claim 1, wherein in the variant with three stablepositions for a first chamber of the at least two pressure chambers apart of the fluid connection is provided by a cover supply duct in thefirst cover, in the ring-shaped part, or between the first cover and thering-shaped part.
 14. A module system as in claim 1, wherein in thevariant with three stable positions a non-pressurized intermediatechamber is separated from the at least two pressure chambers by at leastthe main piston, the ring piston and the ring-shaped part.
 15. A modulesystem as in claim 14, wherein the intermediate chamber is in constantfluid connection with ambient pressure and that the constant fluidconnection is provided at least in part by the breathing duct.
 16. Amodule system as in claim 15, wherein at least a part of the breathingduct is a housing duct in the cylinder housing.
 17. A module system asin claim 13, wherein at least a part of the breathing duct is providedby a cover duct in at least one of the ring-shaped part and said thefirst cover.
 18. A module system as in claim 13, wherein at least a partof the breathing duct is provided by a substantially axial duct in thepiston rod.
 19. A module system as in claim 18, wherein at least a partof the breathing duct is provided by a substantially radial duct in themain piston.
 20. A module system as in claim 15, wherein the cylinderhousing as a finished part is identical for actuator variants with twoand three stable positions, in those three stable position variantswhere the breathing duct is only arranged in one or several of thecover, the piston rod or the main piston.